Many installations of double acting fluid motors that are movable relative to the source of pressure fluid for powering the motors require the use of long lengths of two hoses for supplying high pressure fluid to, and exhausting it from, the motor. The hose lengths are at least as long as the greatest distance obtainable between the fluid source, e.g., the ends of fixed supply lines, and the motor. An example of such an installation is a log crane having a grapple operable by a double-acting hydraulic motor such as is disclosed in U.S. Pat. No. 3,967,736 to Tarassoli. In such installations, the hose lengths necessary to accommodate movement of the grapple may be quite long, e.g., 85 feet. Such long hose lengths necessitate some form of mechanism or system to take up the slack therein, e.g., when the grapple is raised, to prevent damage to the hoses. The take-up system shown in the aforementioned patent merely involves a line attached at one end to the dangling hoses between their ends and thence extended over a pulley to a suspended counterweight. Such a system, while simple, is unsatisfactory in that the hoses rapidly wear at the point of attachment of the line thereto.
A known more sophisticated take-up system for the hydraulic hoses of a log crane involves a movable dual pulley rotating on a horizontal axis and guided for linear movement along a horizontal track located in the overhanging elevated portion of the boom. The hoses are looped over the pulley with one leg of each loop lying in the track and having its end connected to a fixed supply pipe. The other leg overlies the track-supported leg and thence is extended over a fixed pulley to depend to the grapple. A counterweight is attached to the movable pulley by a line extending over a fixed pulley displaced horizontally from the movable pulley opposite the length of the hose loops. This take-up system, while far more efficient and satisfactory than that disclosed in the aforesaid patent, still gives rise to problems. The operating pressure of the double-acting hydraulic cylinders used to open and close the grapple is of the order of 2,000 psi while the lengths of each high pressure hose is of the order of 85 feet. It was found that when such pressure is supplied to the hoses, which are about 1 inch in diameter, they will stretch or elongate about 2% of their length, i.e., about 20 inches. Thus, in operation, when such pressure is supplied to one hose and exhausted from the other, the one hose elongates suddenly about 20" and the other retracts by about the same amount. The sudden elongation, without movement of the grapple, caused corresponding movement of the counterweight to trail the elongation with the result that the counterweight, of the order of two tons, impacted the hose with the movable pulley and stretched it still more. On continued use, it was found that the hoses stretched 22" to 90" and continued to stretch even more until they ruptured.
The following U.S. Pat. Nos. all disclose various types of take-up systems for hoses for supplying fluid under pressure to double-acting fluid motors, but none address the problem encountered by alternate elongation and contraction of the hoses on the supply and exhaust of high fluid pressure therethrough:
Brude et al. 3,474,985 Oct. 28, 1969 PA0 Guinot et al. 3,516,433 June 23, 1970 PA0 Bellings 3,776,403 Dec. 4, 1973 PA0 Dunbar 3,893,480 July 8, 1975 PA0 Ehrhardt 3,968,859 July 13, 1976 PA0 Pugh et al. 4,034,875 July 12, 1977